The invention relates generally to the field of semiconductors. More particularly, the invention relates to the use of single-source tungsten imido precursors in the formation of WNx based films on a substrate, and includes certain tungsten imido complexes and compounds (hereafter xe2x80x9cTICxe2x80x9d) as precursors.
In the manufacture of integrated circuits, barrier layers are often needed to prevent the diffusion of one material to an adjacent material. For instance, when aluminum contacts silicon surfaces, spiking can occur, and when aluminum comes into direct contact with tungsten, a highly resistive alloy can be formed.
Copper is of great interest for use in metallization of VLSI microelectronic devices and has begun replacing aluminum due to copper""s lower resistivity, higher resistance to electromigration, low contact resistance to most materials, and ability to enhance device performance via reduction of RC time delays thereby producing faster microelectronic devices. Moreover, copper may allow a reduced number of metal levels to be necessary because it can generally be packed more tightly than aluminum.
Copper CVD processes which are suitable for large-scale manufacturing and the conformal filling of high aspect ratio inter-level vias in high density integrated circuits are regarded by many as extremely valuable to the electronics and optoelectronics industry, and are therefore being investigated in the art. Unfortunately Cu, like Al, is quite mobile in silicon. Upon direct contact with Si, Cu diffuses and reacts rapidly to form compounds such as Cu3Si. Formation of compounds such as Cu3Si can destroy shallow junctions and contacts during subsequent thermal annealing steps and can result in degraded device performance, or even device failure.
When copper is used as a conductive layer in a device having multi-layer metallization, long-term reliability can only occur if there is little to no interdiffusion between the copper and layers surrounding the copper layer. Copper interdiffusion can result in an increase in contact resistance, change the barrier height, result in leaky PN junctions, cause embrittlement of the contact layer, and destroy electrical connections to the chip. With the increased use of copper as an interconnect material to form high speed integrated circuits, an effective barrier against copper diffusion is required. Diffusion barriers are layers interposed between a material to be isolated (e.g. Cu) and the underlying circuit, and are commonly used in an attempt to prevent undesirable reactions involving the material to be isolated with one or more layers of the underlying circuit.
Research has indicated that nitride barriers are better candidates for reliable diffusion barriers from the interdiffusion standpoint and provide lower electrical resistivities than their pure metal counterparts. Titanium nitride (TiN) has been used as a diffusion barrier for aluminum, but its performance suffers when copper metallization is employed due to excessive copper interdiffusion therethrough. Tantalum nitride (TaN) has generally been the barrier material of choice to date for copper metallization. However, tantalum nitride requires a two-step chemical mechanical polishing (CMP) procedure that results in nearly a one order of magnitude increase in dishing of the copper surface and often results in scratching of the inter-layer dielectric (ILD). Dishing of the copper is caused by a substantially higher CMP etch rate of copper compared to TaN.
Unlike TaN, tungsten nitride (WNx) may be etched using a single CMP process and results in reduced copper dishing relative to copper dishing using TaN as a barrier material because the CMP etch rates of copper and WNx are essentially equal. Tungsten nitride is also known to be an effective diffusion barrier against copper penetration at temperatures of up to approximately 750xc2x0 C. As used herein, WNx is understood to include the numerous tungsten nitride stoichiometries, such as WN, WN2, and W2N. However, there are many other WNx stoichiometries. It is known that WN has a hexagonal crystal structure, WN2 is rhombohedral, and W2N has a face centered cubic structure. Each of the three stoichiometries listed above are thermodynamically stable, but W2N has the lowest resistivity of the three (50 xcexcxcexa9-cm bulk resistivity).
One application for tungsten nitride films is the formation of diffusion barriers between the tungsten of tungsten plugs and adjoining metallization layers on the surface of the wafer, such as copper. Such a diffusion barrier is shown in FIG. 1.
FIG. 1 shows a tungsten plug 14 extending down to a silicon substrate 10 with an overlying copper layer 16 and an intervening diffusion barrier 12. The tungsten plug structure is one example of an application where tungsten nitride has been found as a suitable replacement for titanium nitride, as it is easily formed over the tungsten plug 14.
As feature sizes in integrated circuits have decreased to below 0.25 xcexcm, the necessity for thermally stable, high conformity interface diffusion barriers and gate electrodes has become more important. Deposition of conformal and continuous barrier layers of tungsten nitride at relatively low temperatures on high-aspect-ratio structures is not possible with current processes. The two common methods for deposition of WNx include:
1) physical deposition techniques such as sputtering; and
2) chemical vapor deposition (CVD) from the reaction of tungsten halides and ammonia.
Each above method has associated difficulties. Conventional physical vapor deposition technology involves reactive sputtering from a tungsten target in an atmosphere of gaseous nitrogen with an argon carrier gas. Energized particle techniques, particularly sputtering, generally result in poor step coverage primarily due to shadowing. Applied to small features with high aspect ratios, poor step coverage of the barrier layer may result in areas of excessively thin or missing barrier material allowing copper diffusion into the underlying substrate. Moreover, sputter deposited layers are prone to generate high tensile stress to adjacent layers which may cause defects which may result in degraded device performance and yield loss in integrated circuits.
Current chemical vapor deposition processes for forming WNx generally involve the reduction of tungsten halides such as WF6 and WCl6 by NH3. Although some success has been achieved with halide reduction schemes, at least three major obstacles exist for their use in future generations of integrated circuits. First, the high deposition temperatures ( greater than 700xc2x0 C.) that are required to dissociate tungsten halide molecules are incompatible with most future low dielectric constant materials and some metallization layers. Second, the reaction byproducts (such as HF and HCl) are extremely corrosive and can rapidly etch other exposed device layers (such as Si and SiO2) as well as decrease the operating lifetime of processing equipment. Finally, adduct formation, which can occur when using WF6 and NH3, must be avoided, especially as feature sizes shrink below 0.18 xcexcm. Adduct formation commonly results from gas phase nucleation, as opposed to the desired chemical reaction occurring at the wafer surface.
It is apparent from the above discussion that a need exists for a new process for forming high quality tungsten nitride films which overcomes the problems existing with conventional chemical vapor deposition and physical vapor deposition processes, and which can be used to form a suitable barrier against copper diffusion. The process should be operable at a sufficiently low temperature to avoid copper penetration, limit or avoid generation of corrosive reaction by-products and deposit highly conformal layers capable of filling high aspect ratio structures (e.g. vias).
It would be preferable to utilize a single-source metal organic precursor molecule for the MOCVD (or other suitable deposition technique) of tungsten nitride thin films. The use of suitable metal organics would allow deposition at lower temperatures to ensure compatibility with future low dielectric constant and certain metallization films. The single-source nature of the precursors would allow a simplified reactor delivery system and avoid the possibility of adduct formation that has been reported when WF6 and NH3 are used to form WNx.
Chiu et al. has reported the use of a single-source metalorganic precursor to deposit WN films. [Chiu H. T., S. H. Chuang, J. Mater. Res., 8(6), 1353, (1993]. The precursor used by Chiu was (tBuN)2W(NHtBu)2 (bis(tertbutylimido)bis(tertbutylamido)tungsten), which was delivered via a solid source delivery system. Chiu""s precursor can be classified as a tungsten imido complex having two (2) imido ligands (=NR), the imido groups being covalently bonded to a metal (W). An imido group (=NR) can be defined as a nitrogen atom which is covalently multiply bonded to a metal (e.g. W), with the nitrogen atom also bonded to only one other group (e.g. H, alkyl, aryl, or silyl group). As used herein, the term alkyl includes cyclic alkyls.
An imido group may be contrasted with an amido group, which has the formula NR2. In addition to the covalent bond with the metal, amido groups bear two (2) other substituents (e.g. H, alkyl, aryl, or silyl group). Thus, although Chiu discloses a tungsten imido complex, Chiu""s tungsten imido complex has two (2) imido ligands, as opposed to tungsten imido complexes where tungsten has only a single imido ligand.
Chiu""s depositions were thermal decomposition reactions over a temperature range of 450-650xc2x0 C., but with very slow growth rates of 20-100 xc3x85/min. The resulting films were mainly polycrystalline W2N with lattice parameters of 4.14-4.18 xc3x85. The films had relatively high resistivities of 620-7000 xcexcxcexa9-cm, with marginal step coverage (50-85%) for a 0.40 xcexcm device feature.
The metal organic source reagent should be storage-stable, capable of easy transport to the reactor, possess appropriate decomposition characteristics, and substantially avoid gas phase nucleation. Such a process should preferably result in a highly conformal layer, the layer formed capable of conformal coverage in high aspect ratio features. Importantly, the layer formed should have very low resistivity to avoid impairing the speed of devices incorporating the layer. Deposition rates should also be high to permit efficient production and reduced costs. The increased demand for WNx reagents possessing these properties for use to form improved barriers in metallization schemes, such as copper, necessitates the exploration of novel metal-organic precursors and apparatus and methods for their use.
A source reagent composition for the formation of tungsten nitride films includes at least one single imido tungsten imido species selected from the group consisting of:
i) Tungsten imido complexes of the formula: 
R is selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl, silicon-containing groups of the type SiR1R2R3 and nitrogen-containing groups of the type NR4R5, where R1-R5 are selected from the group consisting of H, Cl, C1-C8 alkyl, aryl and C1-C8 perfluoroalkyl. X is selected from the group consisting of F, Cl, Br, I and N3. L is selected from the group consisting of C1-C8 alkylnitrile, arylnitrile, ether, cyclic ether, heterocyclic aromatic amine, heterocyclic aliphatic amine and alkylamine (NR11R12R13), where R11, R12, R13 are selected from the group consisting of H, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl and silicon-containing groups of the type SiR21R22R23, R21, R22and R23 being selected from the group consisting of H, C1-C8 alkyl, aryl and C1-C8 perfluoroalkyl.
ii) tungsten imido complexes of the formula:
xe2x80x83XyL5-yW(NR) or XyL4-yW(NR)
where R is selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl, silicon-containing groups of the type SiR1R2R3 and nitrogen-containing groups of the type NR4R5. R1-R5 are selected from the group consisting of H, Cl, C1-C8 alkyl, aryl and C1-C8 perfluoroalkyl. X is selected from the group consisting of F, Cl, Br, I, N3 and NR11R12, where R11 and R12 are selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl, silicon-containing groups of the type SiR13R14R15 and nitrogen-containing groups of the type NR16R17, R13-R17 being selected from H, Cl, C1-C8 alkyl, aryl and C1-C8 perfluoroalkyl.
y is an integer between 2 and 4. L is selected from the group consisting of C1-C8 alkylnitrile, arylnitrile, ether, cyclic ether, heterocyclic aromatic amine, heterocyclic aliphatic amine, alkylamine (NR21R22R23), where R21, R22, R23 are selected from the group consisting of H, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl and silicon-containing groups of the type SiR24R25R26, R24, R25 and R26 being selected from the group consisting of H, C1-C8 alkyl, aryl and C1-C8 perfluoroalkyl.
iii) tungsten imido complexes of the formula: 
where R, R1, R2 are selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl, silicon-containing groups of the type SiR3R4R5 and nitrogen-containing groups of the type NR6R7, R3-R7 being selected from the group consisting of H, Cl, C1-C8 alkyl, aryl and C1-C8 perfluoroalkyl.
X is selected from the group consisting of F, Cl, Br, I, N3 and NR11R12, R11 and R12 are selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl, silicon-containing group of the type SiR13R14R15 and nitrogen-containing groups of the type NR16R17, R13-R17 being selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl.
Q is selected from the group consisting of (CH2)2, (CH2)3, and CHxe2x95x90CH. L is selected from the group consisting of C1-C8 alkylnitrile, arylnitrile, ether, cyclic ether, heterocyclic aromatic amine, heterocyclic aliphatic amine and alkylamine (NR21R22R23), where R21, R22, R23 are selected from the group consisting of H, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl and silicon-containing group of the type SiR24R25R26 R24, R25, R26 are selected from the group consisting of H, C1-C8 alkyl, aryl and C1-C8 perfluoroalkyl. L may also be an empty coordination site with no ligand.
iv) tungsten imido complexes of the formula: 
R, R1-R4 are selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl, silicon-containing groups of the type SiR5R6R7 and nitrogen-containing groups of the type NR8R9R5-R9 being selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl.
Q is selected from the group consisting of (CH2)2, (CH2)3 and CHxe2x95x90CH. L is selected from the group consisting of C1-C8 alkylnitrile, arylnitrile, ether, cyclic ether, heterocyclic aromatic amine, heterocyclic aliphatic amine and alkylamine (NR11R12R13), R11, R12, R13 being selected from the group consisting of H, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl and silicon-containing groups of the type SiR14R15R16 where R14, R15, R16 are selected from the group consisting of H, C1-C8 alkyl, aryl and C1-C8 perfluoroalkyl. L may also be an empty coordination site with no ligand.
v) tungsten imido complexes of the formula: 
R, R1-R3 are selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl, silicon-containing groups of the type SiR5R6R7 and nitrogen-containing groups of the type NR8R9, where R5-R9 are selected from the group consisting of H, Cl, C1-C8 alkyl, aryl and C1-C8 perfluoroalkyl.
X is selected from the group consisting of F, Cl, Br, I, N3 and NR11R12, where R11 and R12 are selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl, silicon-containing groups of the type SiR13R14R15 and nitrogen-containing groups of the type NR16R17, R13-R17 being selected from the group consisting of H, Cl, C1-C8 alkyl, aryl, C1-C8 perfluoroalkyl. Q is selected from the group consisting of (CH2)2 and (CH2)3.
In a preferred embodiment, the single imido tungsten imido species is at least one selected from the groups of formulas consisting of XyL5-yW(NR) and XyL4-yW(NR) as specified under (ii), tungsten imido complexes having the formula XyL5-yW(NR) being more preferred. For the more preferred complexes, y is preferably =4.
L can be alkylnitrile. R can be selected from the group of C1-C8 alkyls, aryls and silyls, R being more preferably being selected from the group consisting of isopropyl, t-butyl and cyclohexyl. When R is selected from the group consisting of isopropyl, t-butyl and cyclohexyl, L is preferably an alkylnitrile, more preferably acetonitrile, while X preferably includes Cl.
A source reagent system for the formation of tungsten nitride films includes at least single imido one tungsten imido species having the formula LyW(NR)Xn. R is an alkyl, aryl group or silyl group, y is an integer between 0 and 5, n is an integer between 0 and 4, Ly and Xn being selected from the group of non-imido ligands. The system includes a solvent to dissolve the single imido tungsten imido species. The solvent can be selected from the group consisting of benzonitrile, N-methylpyrrolidinone, dimethyl formamide (DMF), acetonitrile and dimethylacetamide (DMA), more preferably being benzonitrile.
A chemical vapor deposition system having a reactant delivery system for producing and delivering a precursor aerosol includes a reactor, structure for forming a precursor aerosol from a fluid including precursor molecules, and a precursor aerosol delivery conduit in fluid connection with an output of the structure for forming a precursor aerosol. The delivery conduit includes concentric tubes, where the precursor aerosol flows in an inner tube. A structure for controlling the temperature of the volume between the outside of the inner concentric tube and the inside of the outer concentric tube is provided. The reactor is fluidly connected to an output of the inner tube for receiving and decomposing the precursor aerosol.
The structure for forming a precursor aerosol can include a chamber having an input and an output, the chamber including a vibrating plate and structure for introduction of fluid to the chamber input, to form the precursor aerosol. The structure for controlling the temperature can include resistive wire or heat tape.
The system can include a perforated plate having a plurality of channels interposed between the inner tube and the reactor, the perforated plate for improving delivery of the aerosol precursor to the reactor. The diameter of the inner concentric tube increases as the inner concentric tube approaches the perforated plate.
A method for forming tungsten nitride layers on substrates includes the steps of providing at least one single imido tungsten imido species having the formula LyW(NR)Xn, where R is a carbon containing group, y is an integer between 0 and 5, n is an integer between 0 and 4 and Ly and Xn are selected from the group of non-imido ligands. The single imido tungsten imido species is flowed to a surface of a substrate. The single imido tungsten imido species decomposes to form the tungsten nitride layer. A tungsten nitride barrier layer can be formed by this W method. The method can include the step of heating the substrate surface to a temperature of at least 300xc2x0 C. and/or the step of vaporizing the single imido tungsten imido species to form a vapor, the vaporizing step before the flowing step. The flowing step can include flowing of a carrier gas, the carrier gas for aiding transport of the tungsten imido species to the substrate surface. Preferably, the carrier gas includes hydrogen (H2).
The method can include the step of dissolving the single tungsten imido species with a solvent. The solvent is preferably selected from the group consisting of benzonitrile, N-methylpyrrolidinone, dimethyl formamide (DMF), acetonitrile and dimethylacetamide (DMA).
A source reagent composition system for the formation of tungsten nitride films includes at least single imido one tungsten imido species having the formula LyW(NR)Xn, where R is a carbon containing group, y is an integer between 0 and 5, n is an integer between 0 and 4, Ly and Xn being selected from the group of non-imido ligands. R can be an alkyl, aryl or silyl group. L can be selected from the group consisting of C1-C8 alkylnitriles and arylnitriles.